The development of molecular scale electronic applications makes it necessary to generate uniquely tailored and controlled self-assembled monolayers (SAMs), both to facilitate the characterization of new potential molecular constituents and as a path to device fabrication. Conducting and switching molecule SAMs have been postulated as the active elements in field effect transistors. Compounds with nonlinear electronic properties are the focus of single molecule electronics.
U.S. Pat. No. 5,945,832 measured molecular conductivity of compounds using ultra-fine gap electrodes. This method, however, is time-consuming, complicated, and cannot measure more than one compound at a time.
There is a need for a screening technique for determining the conductivity of molecules. The measurement of the conductivity of single molecules is extremely difficult and no readily accessible, simple technique exists for this purpose. Present techniques for measuring the conductivity of single molecules are extremely difficult to execute. Bulk measurements of conductivity measure molecule-to-molecule electron hopping and not single molecule properties.
J. Lu et al (Langmuir, 15, 8184, 1999) used Kelvin probe force microscopy to measure the local contact potential difference of various linear alkanethiol SAM's on gold substrates. A. Dhirani et al (J. Chem Phys, 106, 5249, 1997) showed that SAM's of some alkynethiols on gold substrates exhibited electrical rectifying behavior when probed by scanning tunneling microscopy, whereas alkanethiols and aromatic thiols did not have rectifying characteristics. In none of these cases was the use of surface potential related to molecular conductivity.
The present invention allows for the screening of molecular properties by using the measurement of the surface potential of a self-assembled monolayer of molecules to give an evaluation of the conductivity of those molecules. Scanning surface potential microscopy has been used to measure surface potential variations in patterned SAMs with different terminating groups, allowing the facile screening of the conductivity of molecular structures.